test: refactor exitedAfterDisconnect test

* minor refactoring to conform with test-writing layout guidelines
* rename test to use current terminology rather than deprecated
  terminology
* assert.strictEqual() -> assert.ok()

PR-URL: #16729
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

Author: Trott

test/parallel/test-cluster-disconnect-suicide-race.js test/parallel/test-cluster-disconnect-exitedAfterDisconnect-race.js

@@ -1,8 +1,9 @@
 'use strict';
 
+const common = require('../common');
+
 // Test should fail in Node.js 5.4.1 and pass in later versions.
 
-const common = require('../common');
 const assert = require('assert');
 const cluster = require('cluster');
 
@@ -19,7 +20,7 @@ let eventFired = false;
 cluster.worker.disconnect();
 
 process.nextTick(common.mustCall(() => {
-  assert.strictEqual(eventFired, false, 'disconnect event should wait for ack');
+  assert.ok(!eventFired, 'disconnect event should wait for ack');
 }));
 
 cluster.worker.on('disconnect', common.mustCall(() => {